For reasons of decreasing volume and weight, increasing power density, improving portability and the like, three-dimensional (3-D) semiconductor structures have been developed. However, further improvements for such 3-D semiconductor structures and the methods for forming such 3-D semiconductor structures may still be needed. For example, in a 3-D memory device, stacks comprising alternately stacked conductive layers and insulating layers may be formed for the construction of memory cells. Irregular portions in the layers constituting the stacks caused by defects or other reasons may lead to an undesired failure of the final memory device. As such, a method that can prevent such an undesired failure will be desired.